I am interested to remote control something (sorry for the vagueness) over a distance of several hundred kilometers to a place where there are no internet cables. Therefore, I am interested to know how the US Military remote controlls their drones. My best guess is via satelite communicatation, but wouldn't there be too much lag to make this a feasible option, at least when considering the speed these drones fly with? I also wonder whether such satelite communication is available for civil purposes at a reasonably affordable price?
Try checking out http://www.diydrones.com/ it may answer a lot of your questions.
As for multi-km links RF waves travel at the speed of light which is 299,792,458 meters per second that's more than fast enough for realtime control. The problem with long distance links is that for a frequency high enough to support realtime high-quality video such as microwave frequencies are line of sight for the most part.
In order to get past free space attenuation you'll also need some power over FCC legal limits I'd assume, but you can get past that by getting an amateur radio license. There are ways around this, directional antennas but thats a whole story by itself. (I am not a lawyer, I am however an Amateur Radio Operator)
Free space attenuation of signals (path loss) can be calculated as follows: Lfs = 32.45 + 20 log d + 20 log f
Lfs = Free space loss in dB
d = distance in km
f = frequency in Mhz
Hope this helps!
Microhard http://www.microhardcorp.com/ make nice tiny, light 900Mhz (ISM band) radio modules that bridge ethernet (and serial and USB)
- 1.5Mbps over 90-100km without a repeater.
- Add a repeater every 90-100km, or put the repeater on a tall hill every 300km
- The export restricted versions do 128 bit encryption as well.
- We use the unrestricted module on our robots, which are a lot like US military drones.
- Our old military UAV had an older Microhard radio module (lower bit rates).
- I'm pretty sure most of the short range ( 1-200km) stuff is using the 900Mhz band.
- The module the size of a big matchbox and lightweight.
Why use the 900Mhz ISM band?
- Because it works well, even in built up areas.
- Doesn't need a special radio license to use.
I remember reading an article about how the older drones used an unencrypted wireless signal (apparently they've all now been retrofitted with newer hardware that can support real-time encryption of video).
My guess is they just use a high powered transmitter to send a signal to a base station that can then relay the data with a more traditional network anywhere they need it.
Unfortunately, I don't know where I read this article.